According to J. Med. Chem. 13, 169 (1970) "Compound 26" of the Formula I ##STR1## has been obtained as a "by-product in the preparation of 6 and 7", i.e., the erythro and threo "1-(1,4-benzodioxan-2-yl)-2-aminoethanols", or the 1-(2,3-dihydro-1,4-benzodioxin-2R-yl)-2-amino-1S-ethanol, 1-(2,3-dihydro-1,4-benzodioxin-2R-yl)-2-amino-1R-ethanol and their SR and SS antipodes. The t-butylamino-derivative of said "RR racemate", i.e., the "1-(1,4-benzodioxan-2-yl)-2-t-butylaminoethanol 16 is the most potent .beta.-adrenergic blocking agent yet reported" in said journal, suitable for the treatment or prophylaxis of coronary artery diseases. Accordingly, no strict pharmacological distinction is made between said erythro (or RS) racemates, and the threo (or RR) racemates, and the preparation of the above bis-compound of Formula I as well, which latter must be assumed as inseparable mixture of all 10 possible stereoisomers of the erythro and threo series, i.e., the (SRSR), (RSSR), (SRRS), (RRSS), (RSRR), (SRSS), (RSSS), (SRRR), (RRRR) and (SSSS); the (SRSR) and (RRSS) isomers being the meso-compounds, and the remaining are racemates.
According to a stereospecific process invented by Applicants, designed to afford either erythro or threo isomers, any one of said 10 stereoisomers can now be prepared selectively. Surprisingly it was found that the (SRSR)-meso-compound of Formula II below, belonging to the erythro series, exhibits vastly improved and different pharmacological effects vis-a-vis said known .beta.-adrenergic blocking agent No. 16 of the threo series.